Air conditioning process and apparatus

ABSTRACT

An air conditioning process and apparatus with absorption of water vapor in a circulating absorption liquid containing an aqueous salt solution. The absorption liquid to be supplied to the absorber is cooled by indirect contact with a circulating water stream in a heat exchanger. The circulating water is expanded at reduced pressure to release water vapor and lower the temperature of the water. The water vapor is thereafter absorbed in absorption liquid from the absorber.

FIELD OF THE INVENTION

The present invention relates to an air conditioning process andapparatus in which moisture is removed from air and air is cooled by anabsorption liquid in two absorption stages.

BACKGROUND AND SUMMARY OF THE INVENTION

According to the present invention, air is dehumidified by directcontact with a water-absorbing liquid. An aqueous solution of easilysoluble salts such as, for example, potassium acetate, sodium acetate,potassium carbonate, calcium chloride, lithium chloride, lithium bromideand the like or mixtures thereof is suitably used as the absorptionliquid. These concentrated salt solutions exhibit great affinity towater. Consequently, the water vapor pressure above the solution, iscorrespondingly low.

If air at a certain temperature and a certain relative humidity isbrought into contact with such a concentrated salt solution, water vaporfrom the air is absorbed by the solution as long as the saltconcentration results in a lower water vapor pressure than that presentduring the state of equilibrium.

When air is dehumidified by absorption of water vapor, the absorptionliquid will become increasingly diluted by the absorbed water. As theonly volatile component of the absorption liquid is water, it can beregenerated by evaporation. This is usually accomplished by heating theabsorption liquid to a temperature at which the water vapor pressurethereof exceeds the atmospheric pressure or pressure surrounding it thuscausing the water to evaporate. Concentrated salt-water solutionssuitable for absorption purposes exhibit a high boiling point elevation.Generally, the dilution of the absorption liquid by absorption of watervapor is relatively small. Consequently, evaporation in more than onestage or effect is usually not feasible so that the diluted absorptionliquid is usually regenerated by evaporation in a single stageevaporator.

To regenerate the absorption liquid in an evaporator an amount of energycorresponding to the heat of vaporization is required. Additional energyis needed to heat the liquid to its boiling temperature and tocompensate for heat losses and the like.

The present invention utilizes the low water vapor pressure above aconcentrated water-salt solution to absorb a saturated water vapor inthe salt solution at a higher temperature.

According to the present invention, an absorption liquid which is usedin an absorber having one or more absorption stages or zones in an airconditioning system is cooled by a circulating water stream in a heatexchanger. The water stream which takes up and carries away heat fromthe heat exchanger is caused to expand at reduced pressure, for example,in a flash tank. An amount of water vapor corresponding to thetemperature drop, i.e. the absolute pressure is then released. The watervapor released by expansion in the flash tank is introduced into acondenser having surfaces which are continuously wetted by awater-absorbing salt solution. The salt solution used in the condensermay be from any suitable source, but preferably is the salt solutionused as an absorption liquid in the absorber and which is circulatedthrough and cooled in the heat exchanger. Water vapor is absorbed by thesalt solution or condensed into it as long as the water vapor pressureabove the salt solution is lower than the pressure of the vapor releasedby the expansion from the flash tank. It is thus possible to condensewater vapor in a salt solution having a temperature which is about 20°C. or more above the saturation temperature of the water vapor.

It is, accordingly, an object of the present invention to provide amethod of producing low air temperatures and low absolute humidities inair conditioning systems.

It is another object of the present invention to improve the efficiencyand to lower the energy consumption of air conditioning systems usingabsorption technique.

These and other objects and advantages of the present invention will beapparent from the following detailed description and the accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic flow diagram illustrating an air conditioningsystem in which a water-absorbing salt solution is used fordehumidification and cooling of air in two absorption stages.

FIG. 2 is a vertical cross-sectional view of condenser 105 of FIG. 1;and

FIG. 3 is a cross-sectional view along the lines 3--3 of the condensershown in FIG. 2.

DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENT

As shown in FIG. 1 the air conditioning system comprises an absorber 100having two absorption zones or stages 101 and 102, a heat exchanger 103,a flash tank 104, a first condenser 105, a second condenser 106, anevaporator 107, a cooler 108 and a second heat exchanger 134. It will beunderstood that although FIG. 1 shows absorption zones 101 and 102 asseparate units, both absorption zones could be incorporated in oneapparatus. Also, more than one absorber could be used.

Air flowing through a conduit 109 is brought into direct contact with atleast a part of the concentrated absorption liquid supplied throughconduit 110 to absorption stage 101. A second part of the concentratedabsorption liquid fed to absorption stage 102 is first cooled in heatexchanger 103 by indirect contact with a circulating water stream takingup heat and carrying it away. As in shown in FIG. 1, absorption liquidmay be circulated through absorption stage 102 and heat exchanger 103thus leading to absorption at constant relative humidity. Water isintroduced into heat exchanger 103 through conduit 112 and is dischargedtherefrom through conduit 113. The heated water discharged from heatexchanger 103 is passed via pressure control device such as restrictionvalve 155, to flash tank 104 in which the pressure is sufficiently lowso as to cause the release of water vapor therefrom. Evaporation ofwater requires heat which is removed from the water causing thetemperature thereof to decrease. An amount of vapor corresponding to thetemperature drop of the water is released. The vapor is thereafterdischarged from flash tank 104 and passed to the first condenser 105through conduit 114. The remaining water is recirculated to heatexchanger 103 preferably by a pump 115 through conduit 116. As water iscontinuously consumed by evaporation, additional water is suppliedthrough conduit 117 as needed.

As shown in FIGS. 2 and 3, first condenser 105 comprises preferably aplurality of preferably vertically oriented tubular heat exchangeelements 118 each having a first inner surface 118a and a second outersurface 118b. The heat exchange elements are enclosed in a casing 119having an inlet 120 for vapor to be condensed, an inlet 121 for entry ofabsorption liquid, and an outlet 122 for absorption liquid diluted bycondensate from the condensing water vapor. Condenser 105 is furtherprovided with an air inlet 123 and an air outlet 124. An outlet 125 isprovided for the removal of uncondensed gases or water vapor. A vacuumpump (not shown) may be connected to outlet 125.

An upper tube sheet or plate 126 and a lower tube sheet 127, to whichthe upper and lower end of each heat exchange element is attached, form,together with the respective parts of the vertical wall of the casing,an enclosed space 128. A plate 129 is positioned below the upper tubeplate so that a gap is formed around the outer surface 118b of the heatexchange elements so that the absorption liquid supplied through inlet121 is caused to flow down preferably uniformly along the outer surfaceof each heat exchange element in the form of a thin liquid film. Animpeller 130 in the upper end of the casing 119 causes air to be drawnup through the heat exchanger means.

The water vapor released in the flash tank 104 by expansion is passedthrough conduit 114 to inlet 120 of the condenser 105 communicating withthe space around the outer surface of the heat exchange elements 118defined by upper and lower tube sheets 126 and 127 and the vertical wallof the casing 119. The water vapor contacts the absorption liquid whichis discharged from absorption zone 102 through conduit 131, and ispassed to inlets 121 and made to flow down preferably uniformly alongthe outer surfaces 118b of the heat exchange elements.

The water vapor supplied to the condenser 105 through inlet 120condenses on the outside surfaces of the heat exchange elements and isremoved preferably by means of a suitable pump (not shown) along withthe absorption liquid through outlet 122. As long as the temperature ofthe absorption liquid and its concentration are such that the watervapor pressure above the liquid is lower than that of the water vapor,the water vapor will be absorbed by the absorption liquid. Dilutedabsorption liquid is transferred to evaporator 107 through conduit 132and 133 via a heat exchanger 134. The heat released by condensation ofthe water vapor will be taken up by the air following through inlet 123over the inner-surfaces 118a of the heat exchange elements of condenser105 and will be removed along with the air exiting through outlet 124.

At least a portion of the absorption liquid which has taken up moisturefrom the air in absorption stage 101 is discharged through conduit 135and is directed through a branchconduit 136 to second condenser 106.Second condenser 106 includes preferably a plurality of preferablyvertically disposed spaced apart heat exchange elements 137 which arecomposed of pairs of parallel plates which are connected at their edgesto form a plurality of closed spaces within the casing or housing 119.Other conventional heat exchange elements such as tube-type exchangersmay also be utilized. Open channels are formed between the heat exchangeelements. The interiors of each heat exchange element are connected attheir upper end to an inlet 138 for water vapor and at their lower endto an outlet 139 for condensate. Distributors 140 provided with aplurality of openings or spray nozzles extend lengthwise across thehousing above each heat exchange element so as to form means fordistributing absorption liquid preferably substantially uniformly overthe outer surfacess of the heat exchange elements.

Accordingly, a portion of the diluted absorption liquid to beconcentrated by evaporation is fed from absorber 101 to second condenser106 through branchconduit 136 and is introduced into distributor means140 disposed above each heat exchange element 137 of condenser 106 so asto cause the absorption liquid to flow down preferably in form of auniform thin film over the outer surface of heat exchange elements 137.Water vapor supplied through conduit 141, preferably connected to thetop of housing 142 of evaporator 107 enclosing one or more heat exchangeelements 143, is introduced through inlet 138 into heat exchangeelements 137. Although the water vapor is preferably taken fromevaporator 107, vapor from other sources may also be utilized. Use ofthe vapor exiting from evaporator 107, however, results in an additionalevaporator effect. Thus, if the number of evaporators 107 used isrepresented by the letter n, the process of the preferred embodiment ofthe present invention results in n+1 evaporation effects or stages. Theabsorption liquid flowing down along the outer surfaces of the heatexchange elements 137 will be heated by indirect contact with the hotwater vapor exiting from evaporator 107. The air which is suppliedthrough inlet 123 and flowing through the casing 119 on the outside ofthe heat exchange elements of second condenser 106 will, by directcontact with the absorption liquid, lower the vapor pressure of theabsorption liquid and cause evaporation of water therefrom. The watervapor is removed together with the air flowing out from the condenserthrough the outlet 124. The amount of scavenger air required for coolingthe absorption liquid without evaporative cooling is about ten timesgreater than with evaporative cooling as described. The scavenger airflowing through housing 119 through inlet 123 is thus carefullybalanced. Generaly, about 90% of the air introduced into inlet 123 maybe withdrawn prior to the air coming into contact with condensers 105and/or condenser 106. The withdrawn air stream is not indicated in thedrawing.

Evaporation of water from the absorption liquid requires heat energywhich is removed from the water vapor inside the heat exchange elements137 causing the vapor to condense therein. At least a portion of thecondensate which will form within the heat exchange elements 137 byindirect contact of the water vapor with the absorption liquid isremoved through outlet 139 and is passed through conduit 144 to cooler108 disposed preferably in the lower part of housing 119 as is morefully described below. Another portion of the condensate collected incondenser 106 is fed to distributor 156 through branchconduit 158 foruse as a cooling liquid to flow down in form of a thin liquid filmpreferably uniformly over the inner surfaces 118a of each heat exchangeelement 118 of condenser 105. Additional cooling water may be added tothe system, as required, through inlet 160.

Absorption liquid preconcentrated by evaporation of water therefrom isdropping down into container or vat 145 preferably disposed below thelower ends of the heat exchange elements 137. The preconcentratedabsorption liquid is then fed to evaporator 107 through conduit 133preferably via heat exchanger 134 to raise the temperature thereof priorto the entry into the evaporator by indirect contact with concentratedabsorption liquid previously withdrawn from the evaporator.

The evaporator comprises preferably a plurality of heat exchangeelements 143 which may be of similar to construction as to those of thecondenser 106 having an inlet 146 and an outlet 147 for a heating fluidsuch as flue gas, hot water or steam. Distributor means 148 disposedabove the upper ends of the heat exchange elements 143 suppliesabsorption liquid preferably uniformly to the outside surface of theheat exchange elements. The absorption liquid will be heated to itsboiling point whereupon water will evaporate from the absorption liquidwhich is flowing down over the surface of the heat exchange elements.The concentrated absorption liquid collected at the bottom of thehousing 142 is withdrawn from the evaporator through a discharge conduit149. At least a portion of the concentrated absorption liquid may berecirculated to the distributor means 148 through conduit 150. Theremainder of the concentrated liquid is passed through conduit 151 viathe heat exchanger 134, branchconduits 152 to absorption stage 101 viacooler 108 and through branchconduit 153 to absorption stage 102 viaheat exchanger 103.

The water vapor generated in casing 142 of evaporator 107 by evaporationof the absorption liquid on the surface of the heat exchange elements143 is withdrawn from the evaporator and passed through conduit 141 tocondenser 106 to be condensed therein and to serve as a heating mediumfor preconcentrating the absorption liquid.

The absorption liquid fed to cooler 108 is introduced into heat exchangeelements 154 which may be of similar design as those of the secondcondenser 106. The heat exchange elements of the cooler are preferablydisposeed below those of the first condenser 105. The absorption liquidis brought into indirect contact with a cooling liquid supplied by adistributor means 157 disposed above heat exchange elements 154 and iscaused to flow down in form of a thin liquid film preferably uniformlyover the outer surfaces of the heat exchange elements 154. The coolingliquid mainly comprises the condensate from condenser 106. It is anadditional advantage of the present invention that the condensate fromcondenser 106 may be utilized as the cooling liquid on the heat exchangeelements of cooler 108 and condenser 105. The use of this condensate isparticularly advantageous because it comprises substantially distilledwater thus avoiding encrusts and deposits on the heat exchange surfacesof heat exchange elements 154 of cooler 108 and heat exchange elements118 of condenser 105.

The heat exchange elements of condenser 106, 105 and cooler 108 and thecasing 119 preferably form a cooling tower through which air is drawn bymeans of impeller 130. The air flowing through casing or housing 119over the outside of the heat exchange elements 154 of cooler 108 indirect contact with the outside surfaces wetted by the cooling liquidwill cause evaporation of the cooling liquid. The evaporated water isremoved by the air flow. Evaporation of water, in turn, causes removalof heat which is taken from the absorption liquid inside heat exchangeelements 154. The cooled absorption liquid is then passed to the firstabsorption stage 101 through conduit 110.

As pointed out, at least a portion of the condensate exiting condenser106 may be fed to the space above the upper tube plate 126 of firstcondenser 105 and caused to flow down as a liquid film over the innersurfaces of heat exchange elements 118 so as to cause evaporativecooling leading to a more efficient cooling process, particularly incombination with the air flow entering housing 119 through inlet 123.Additionally, the humidity and the temperature of the air stream inconduit 109 can be controlled by spray water which is made to evaporatein the air stream.

EXAMPLE

8,100 kg/h of air to be treated is fed to absorbers 101 and 102 throughconduit 109 under the following conditions: t=30/27° C.; x=0.021; i=83kJ/kg.

About 140 kg/h of water is removed in absorption stages 101 and 102. Thetemperature in absorption stage 101 is maintained (isothermalabsorption) by circulating 37,300 kg/h absorption liquid which has beencooled by about 50,000 kg/h of air in cooler 108. During the coolingstep in cooler 108 the condition of the scavenger air has changed asfollows: from t=30/29° C.; x=0.026 to t=31.5°/30.5° C. and x=0.031before entering first condenser 105.

In condenser 105, water vapor at 15° C. and 0.017 bar is absorbed in anabsorption solution having a temperature of about 41° C. whichcorresponds to that water vapor pressure. The absorbed water adds about70 kg water to the absorption solution. The absorption solution is thencooled with the scavenger air thereby changing the temperature of theair from 31.5° to about 38° C. No change in the water content of the airwill take place as the air passes over the opposite side of the heatexchanger surface rather than over the absorption solution.

The conditions in second condenser 106 may be as follows. The vapor isexiting evaporator 107 in a super heated state at 1 bar and 145° C. Incondenser 106 condensation occurs at 1 bar and 100° C. Evaporativecooling is achieved by feeding absorption liquid through distributor 140over the outer surface of the heat exchange elements 137. The absorptionliquid has been preheated by heat exchange (not indicated in thedrawing) to about 83° C. and the liquid film over the heat exchangesurfaces has reached a temperature of about 88° C. The actual watervapor pressure above the film of absorption liquid will be about 150 mmHg. 13,700 kg/h of the 50,000 kg/h of scavenger air having passsed overcondenser 105 will be passed over condenser 106 resulting in theevaporation and removal of about 90 kg/h of water as vapor. Theremainder of the scavenger air is by-passed or withdrawn prior toreaching condensr 106 (not shown in the drawing). The remainder of thewater, about 120 kg/h, is evaporated in evaporator 107 and fed tocondenser 106. In accordance with the present invention it is thuspossible to evaporate about 210 kg/h of water with the energy demandrequired for the evaporation of about 120 kg/h of water.

It should be understood that the preferred embodiment and exampledescribed above is for illustrative purposes only and is not to beconstrued as limiting the scope of this invention which is properlydelineated in the appended claims. While the invention has been hereinshown and described as what is presently conceived to be the mostpractical and preferred embodiment thereof, it will be apparent to thosehaving ordinary skill in the art, that many modifications may be madethereof within the scope of the invention.

What is claimed is:
 1. A process for conditioning aircomprising:directly contacting air in an absorber having a first andsecond absorption zone with an absorption liquid circulated through saidfirst and second zones, said absorption liquid comprising an aqueoussalt solution; cooling said absorption liquid circulated through saidsecond absorption zone by indirect contact with circulating coolingwater in a heat exchanger; discharging said cooling water from said heatexchanger; expanding said cooling water discharged from said heatexchanger at reduced pressure to convert at least part of said coolingwater into cooling water vapor, and recirculating the remaining coolingwater to said heat exchanger; condensing said cooling water vapor andabsorbing said cooling water vapor into said absorption liquid to dilutesaid absorption liquid, said absorption liquid having a lower watervapor pressure than said cooling water vapor; concentrating said dilutedabsorption liquid by evaporation in the evaporator; and recirculatingsaid concentrated absorption liquid to said absorber.
 2. The process ofclaim 1, wherein said cooling water vapor is absorbed into saidabsorption liquid on a first cooling surface of a heat exchange elementand cooling a second surface in heat exchange relationship with saidfirst surface by an air stream flowing along said second surface.
 3. Theprocess of claim 1, further comprising:heating at least a portion ofsaid absorption liquid exiting said first absorption zone to the boilingpoint thereof by indirect heat exchange with a heating fluid in anevaporator to form water vapor; condensing said water vapor with acooling liquid in a condenser; utilizing as a cooling liquid in saidcondenser absorption liquid which is concentrated in said evaporator;circulating air through said condenser in contact with said absorptionliquid to lower the vapor pressure thereof; and recirculating saidconcentrated absorption liquid from said evaporator to said absorber. 4.The process of claim 3, wherein said absorption liquid is concentratedin said evaporator prior to the utilization thereof as a cooling liquidin said condenser.
 5. The process of claim 3, wherein the absorptionliquid is concentrated in said evaporator after it has been utilized asa cooling liquid in said condenser.
 6. The process of claim 3, furthercomprising:cooling at least a portion of said absorption liquid bybringing said liquid into indirect heat exchange relation with a coolingliquid on a cooling surface; utilizing as a cooling liquid on saidcooling surface the condensate formed by condensing said water vaporfrom said evaporator; evaporating water vapor from said condensate to anair stream; and recirculating said cooled absorption liquid to saidabsorber.
 7. The process of claim 1, wherein said absorption liquid isan aqueous solution comprising potassium acetate, sodium acetate,potassium carbonate, calcium chloride, lithium chloride, or lithiumbromide or mixtures thereof.
 8. An apparatus for conditioning aircomprising:an absorber having two absorption zones for directlycontacting an air stream with circulating absorption liquid; a heatexchanger in communication with said absorber for transferring heat fromsaid absorption liquid circulated through said second absorption zone toa circulating stream of cooling water; a flash tank for releasing watervapor from said stream of cooling water; first means in communicationwith said second absorption zone and said flash tank for condensing saidwater vapor released from said cooling water comprising a first heatexchange element having a cooling surface for condensing and absorbingsaid water vapor into said absorption liquid; means for maintaining areduced pressure in said tank and over said cooling surface of saidfirst condenser means; means for circulating water through said heatexchanger and said flash tank; and first passage means for transferringabsorption liquid and condensate from said first condenser means to anevaporator for concentrating said absorption liquid.
 9. The apparatus ofclaim 8, further comprising:means for evaporating said absorption liquidcomprising a second heat exchange element for generating water vapor byvaporization of said absorption liquid exiting said first condensermeans; said second heat exchange element comprising a first and secondsurface for concentrating said absorption liquid on said first surfaceby addition of heat to said second surface of said second heat element;second means for condensing absorption liquid comprising a third heatexchange element having a first and a second surface for generating acondensate by condensing vapor on said first surface of said third heatexchange element with transfer of heat to said absorption liquid exitingfrom said first absorption stage for preconcentration on said secondsurface of said third heat exchange element; means in communication withsaid second condenser means for introducing an air flow for vaporizingsaid absorption liquid by simultaneously lowering the water vaporpressure thereof on said second surface of said third heat exchangeelement; second passage means for transferring said preconcentratedabsorption liquid from said second condenser means to said evaporatormeans; third passage means for transferring said water vapor from saidevaporator means to said second condenser means; fourth passage meansfor transferring said concentrated absorption liquid from saidevaporator means to said absorber.
 10. The apparatus of claim 9, furthercomprisingmeans for cooling absorption liquid comprising a fourth heatexchange element having a first and a second surface for cooling saidliquid on said first surface of said fourth heat exchange elements withtransfer of heat to said condensate on said second surface of saidfourth heat exchange element; means in communication with said coolingmeans for introducing an air flow for simultaneously lowering the watervapor pressure of said condensate; fifth passage means for transferringsaid condensate from said second condenser means to said cooler means;sixth passage means for transferring cooled absorption liquid from saidcooler means to the said first absorption zone.
 11. The apparatus ofclaim 10, wherein said first heat exchange element of said firstcondenser means is disposed above said fourth heat exchange element ofsaid cooler means and said third heat exchange element of said secondcondenser means is disposed above said first heat exchange element, allsaid heat exchange elements being disposed within the same housing. 12.The apparatus of claim 9, further comprising seventh passage means fortransferring said condensate from said second condenser means to saidfirst condenser means.